Insights into the role of defect engineering for photocatalytic mercury removal from flue gas: A review

Semiconductor defect engineering provides an effective scheme for improving the efficiency of photocatalytic oxidation of Hg0 to Hg2+. This article mainly reviews the latest progress in photocatalyst defect engineering for photocatalytic mercury removal. The basic principles and mechanisms of photocatalysis and photon induced Hg0 oxidation are briefly summarized, including the related properties of elemental mercury, reaction pathways, and quantitative methods for mercury conversion. Subsequently, a brief summary of defect classification, synthesis strategies, and identification techniques is provided. The research progress of in situ characterization techniques for monitoring the state of defects in the Hg0 oxidation process is introduced. Particular emphasis was placed on various surface defect strategies and their key roles in improving the photocatalytic oxidation performance of Hg0, including surface vacancies (i.e., anionic and cationic vacancies), heteroatom doping i.e., metal element doping and non-metallic element doping, and atomic defined surface sites. Finally, the future opportunities, challenges, and prospects for further development of defective engineering photocatalysts for photocatalytic mercury removal are prospected. The results of this study are expected to provide profound guidance for the further design of photochemical fixed defect engineering catalysts with high activity and stability.